DISSOCIATION OF CYCLIC INOSITOL PHOSPHOHYDROLASE ACTIVITY FROM ANNEXIN-III

Cyclic inositol phosphohydrolase is a phosphodiesterase that cleaves t he cyclic bond of cyclic inositol monophosphate, In 1990, Boss ct at ( Boss, T. S., Tait, J. F., and Majerus, P. W. (1990) Science 248, 605-6 07) purified this enzyme from human placenta and reported that cyclic inositol phosphohydrolase is identical to annexin III, Independent con firmation of this finding has not been provided. The relative distribu tion of annexin III and cyclic inositol phosphohydrolase activity in r at kidney and spleen indicated that annexin III can be dissociated hom cyclic inositol phosphohydrolase activity, Rat spleen contains large quantities of annexin III, but has very little cyclic inositol phospho hydrolase activity, In contrast, rat kidney, one of the richest source s of cyclic inositol phosphohydrolase activity, possesses very little (immunohistochemistry) or no (Western blot) annexin IIIm. similar to c ytosol of human placenta, cytosol of guinea pig kidney contains both a nnexin III and cyclic inositol phosphohydrolase. On SDS-gel electropho resis, guinea pig kidney annexin III has a slightly different mobility than the human placental annexin III. Human placental annexin III co- migrates with cyclic inositol phosphohydrolase on ion exchange chromat ography, while guinea pig kidney annexin III is clearly dissociated fr om cyclic inositol phosphohydrolase on ion exchange chromatography. Bo th guinea pig kidney annexin III and human placental annexin III pelle t with the addition of calcium and centrifugation, while cyclic inosit ol phosphohydrolase activity in both of these tissues remains in the s upernatant. Our studies clearly show that cyclic inositol phosphohydro lase and annexin III are two different proteins.